Focusing on the second year of life, this research is concerned with processes that govern the early stages in personality development. The strategy involves first taking a detailed look at what babies actually do in interaction with their mothers, their peers, and the world of objects; then, anchored in this broad observational base, formally modeling alternative explanations of behavioral change in social and exploratory behavior. To attain the data base, repeated observations of second year behavior in a variety of naturalistic and semi-structured situations were recorded and stored, mainly on videotape. In subsequent viewings, coding systems for abstracting a broad spectrum of behaviors were devised, giving rise to extensive sets of discrete, unambiguous, yet complexly defined behavioral indices. Follow-up observations at age 3 1/2 were made in the course of a 5-week nursery school program; these were recorded in terms of rating scale and Q-sort placements. Data analysis originates in models of qualitative developmental change. To derive measures of functioning at a particular developmental stage, mutually exclusive classes of behavioral indices are delineated; the sample is then partitioned into classes of individuals who are similar in the attributes latent within the observable quantities. Developmental sequences of thus obtained latent structures are examined and alternate hypotheses concerning the necessary dependencies within and among sequences are modeled. Behavior with peers, objects, and mother are to be sequentially submitted to analysis, the final stages of the project being devoted to modeling understanding of that which integrates developmental change across these three domains. The specific aims include delineating facets of behavior in which individually enduring patterns are established and identifying factors which contribute to their development; establishing sequences of developmental phases and examining conditions necessary for their branching into different paths of progression; and determining whether the construct of "competence" is productive in conceptualizing individual differences in personality development.